1. Field of Invention
The present invention generally relates to image recorders, i.e. devices which record images on photosensitive media, examples of which devices include laser printers, plotters, and platesetters.
The present invention particularly relates to improved registration between successive images produced in and by such an image recorder.
2. Background of the Invention
Typically image recorders are constructed wherein a laser beam sweeps across a photosensitive medium while the medium moves slowly in a direction perpendicular to the primary direction of laser beam scanning. Such imager recorders are limited when diazo or photopolymer media are to be imaged (e.g. printing plate material) with ultraviolet light inasmuch as lasers suitable for generating the large intensities of ultraviolet light required are not economically available.
In the above-mentioned co-pending U.S. patent application Ser. Nos. 811,807 for an IMAGING DEVICE; 811,806 for a HIGH RESOLUTION IMAGING DEVICE; and 811,797 for a FAULT TOLERANT IMAGING DEVICE it is taught that small rectangular images may be created by the use of Deformable Mirror Modules, such as are also described in U.S. Pat. No. 5,028,939 to Hornbeck, et al., to deflect a beam of intense ultraviolet light generated by an incandescent, non-laser, light source.
The co-pending related patent applications also disclose an adjustment of the optical path of the imaging in order to improve the spatial registration, one region to the next, of each of a number of successively exposed image regions. The optical path adjustment preferably transpires by use of a tiltable glass plate. The adjustment compensates for positional errors in the location of the successive, and successively exposed, image regions.
The optical path adjustment is performed responsively to sensed registration marks. These registration marks are normally emplaced on diazo printing plate media or photopolymer-based proofing materials--the recording of which immediately produces a visually sensible change--at the same time, and through the same optical path, as the successive image regions are successively exposed. The recording of the registration marks is with one optical system, and the later sensing of the recorded registration marks is with another optical system.
It would be useful if, in addition to the compensation of the optical path in the exposures of the successive images in order to accord for inaccuracies in the movement of the medium, any positional errors resultant from the movement of the medium could be minimized, and prevented from accumulating. Accordingly, some feedback control of the transport of the medium in order to minimize positional errors--as well as (presumptively optical path) compensation for uneliminatable positional errors--would be desirable.